The present invention relates generally to devices for curing light-hardening polymer dental filling material, and more particularly to a focusing tip configured to be attached to the end of a dental curing light.
Light-hardening polymer dental material has enjoyed wide success in providing a dental filling material that is the same or nearly the same color as the patient's tooth. Fillings made with the naturally colored resin are less noticeable, compared to similar amalgam-type fillings. However, amalgam fillings continue to be used in some instances, such as on posterior teeth (i.e. bicuspids and molars) where the cosmetic detraction of the amalgam filling is less noticeable.
Dental amalgam is a mechanical mixture of mercury and powdered silver alloy. The firm consistency of dental amalgam makes restorations relatively easy to place, to form tight contacts, and to provide tight margins. Dental amalgam provides excellent wear and has a proven record of biological compatibility.
Filling material is generally pressed into a cavity prepared by the dentist. If a portion of the cavity is coextensive with a sidewall of the tooth, a matrix band is typically used to provide an outer surface when filling the cavity. The matrix band is a thin band of metal or plastic that the dentist tightens around the tooth being filled. It is resilient, and generally conforms to the perimeter of the tooth. Amalgam filling can be packed into the cavity and against the matrix band, and after the amalgam condenses, the matrix band is removed. The contact between the filled tooth and the adjacent tooth is preserved with amalgam filling material because the amalgam is firm and retains its shape after condensation.
Polymer-based filling material flows differently than amalgam and cannot be packed into a cavity in the same manner to condense in the shape defined by the matrix band. Light-cured fillings do not go through a gradual hardening phase during which they can be carved into a desired shape. They are too soft at placement and too hard after light hardening, whereas silver amalgam filling can be finished with hand carving instruments as they harden. Light-cured filling material is typically shaped after hardening with metal burs or fine diamond-coated burs.
Light-cured white fillings depend on a tight, hard bond with the tooth material, otherwise leakage and decay will result. The filling material should be fully cured, which can be difficult because the curing light might not completely penetrate thick fillings. However, the light-cured filling material can be built up in several layers with intermediate curing steps. It is similarly more difficult to use light-cured filling material to form contacts between teeth. Contacts are preferably tight, and open contacts allow foods to pass through while chewing, which gets stuck between the teeth. Food stuck between the teeth can be annoying, and can cause periodontal or gum problems.
Techniques have been developed to cure polymer-based filling by pressing the matrix band against the adjacent tooth while light curing the polymer filling material in the cavity. A small light-transmitting cone is pressed against the inside of the matrix band to hold it against the adjacent tooth. Sometimes, dental wedges are used to spread the teeth apart while the matrix band is placed and the cavity filled. This allows more filling material to be placed between the teeth. A second application of polymer filling material is then placed in the secondary cavity formed by the cone used to hold the matrix band against the adjacent tooth, and the second application of polymer filling material is light hardened. After removal of the wedge and matrix band, the teeth will return to their preoperative position and form a tight contact.
Unfortunately, conventional cones are relatively large, making them difficult to manipulate in a patient's mouth. This shortcoming is particularly noticeable when attempting to use light-cured filling material in posterior teeth. It is important to obtain a thorough cure of the resin in posterior teeth because of the pressures and stresses they must endure. Some conventional cones reduce the light intensity reaching the filling material, which requires the dentist to hold the light on the filling longer, further complicating the procedure. The cones also leave a straight-sided void in the first application of filling material, and some do not efficiently transmit light to the preparation region. Inefficient transmission of light to the filling material can result in incomplete hardening of the filling material for a given time, or require additional time in the patient's mouth. Thus, existing cones and similar devices have undesirable size, shape, and transmission characteristics.